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+--- Thread: Default value of a type at Runtime (/Thread-Default-value-of-a-type-at-Runtime)
Default value of a type at Runtime - interpulmonary503175 - 07-24-2023
For any given type i want to know its default value.
In C#, there is a keyword called default for doing this like
object obj = default(Decimal);
but I have an instance of Type (called myType) and if I say this,
object obj = default(myType);
it doesn't work
Is there any good way of doing this?
I know that a huge switch block will work but thats not a good choice.
RE: Default value of a type at Runtime - greaseproofness134086 - 07-24-2023
How about something like...
class Program
{
static void Main(string[] args)
{
PrintDefault(typeof(object));
PrintDefault(typeof(string));
PrintDefault(typeof(int));
PrintDefault(typeof(int?));
}
private static void PrintDefault(Type type)
{
Console.WriteLine("default({0}) = {1}", type,
DefaultGenerator.GetDefaultValue(type));
}
}
public class DefaultGenerator
{
public static object GetDefaultValue(Type parameter)
{
var defaultGeneratorType =
typeof(DefaultGenerator<>).MakeGenericType(parameter);
return defaultGeneratorType.InvokeMember(
"GetDefault",
BindingFlags.Static |
BindingFlags.Public |
BindingFlags.InvokeMethod,
null, null, new object[0]);
}
}
public class DefaultGenerator<T>
{
public static T GetDefault()
{
return default(T);
}
}
It produces the following output:
default(System.Object) =
default(System.String) =
default(System.Int32) = 0
default(System.Nullable`1[System.Int32]) =
RE: Default value of a type at Runtime - gonad98 - 07-24-2023
What do you mean by "Default Value"? All reference Types ("class") have null as default value, while all value types will have their default values according to [this table][1].
[1]:
[To see links please register here]
RE: Default value of a type at Runtime - wilhelmina140 - 07-24-2023
Here's a function that will return the default value for a nullable type (in other words, it returns 0 for both `Decimal` and `Decimal?`):
public static object DefaultValue(Type maybeNullable)
{
Type underlying = Nullable.GetUnderlyingType(maybeNullable);
if (underlying != null)
return Activator.CreateInstance(underlying);
return Activator.CreateInstance(maybeNullable);
}
RE: Default value of a type at Runtime - piccolo283 - 07-24-2023
You could also add it as an extension method to System.Type:
public static class TypeExtensions
{
public static object GetDefaultValue(this Type t)
{
if (t.IsValueType && Nullable.GetUnderlyingType(t) == null)
return Activator.CreateInstance(t);
else
return null;
}
}
RE: Default value of a type at Runtime - ectolophlobbb - 07-24-2023
There's really only two possibilities: `null` for reference types and `new myType()` for value types (which corresponds to 0 for int, float, etc) So you really only need to account for two cases:
object GetDefaultValue(Type t)
{
if (t.IsValueType)
return Activator.CreateInstance(t);
return null;
}
(Because value types always have a default constructor, that call to Activator.CreateInstance will never fail).